1. Technical Field
This disclosure relates to an optical recording medium (hereinafter referred to as an “optical recording medium,” “information recording medium,” or “optical disc” in some cases) more particularly to a method of recording to rewritable optical discs such as CD-RWs, DVD-RWs, DVD+RWs and DVD-RAMs in which a phase-change material is used as a recording layer, and to an optical recording medium to which the recording method can be applied.
2. Description of the Related Art
Rewritable optical discs applied with a phase change technology, as typified by CD-RWs, DVD+RWs and DVD-RWs, are widely used for audio-visual purpose and information recording purpose in computers. With an increase in the digital capacity in recent years, the recording speed for these optical discs is also expected to be increased.
High-speed recording for these optical discs using the phase-change technology requires excellent rewriting performance both at higher scanning speeds and in a broader scanning speed range—the former corresponds to the maximum recording speed and the latter to the speed range inside of which recording is possible. For the latter, in particular, a speed ratio of about 2.4:1 (maximum speed: minimum speed) is required to support the CAV (Constant Angular Velocity) recording, a technology that is necessary for the acceleration of random access recording. In the CAV recording, the scanning speed v varies with the recording radial position r, i.e., v/r=constant, and thus recording needs to be possible at any recording speed below the maximum recording speed. Furthermore, the higher the maximum speed, the broader the scanning speed range, inevitably, e.g., 4×DVD+RW discs require a scanning speed range of 5.8 m/s to 14.0 m/s to support the CAV recording. Thus, further development is required for optical recording media and recording methods, so that recording is possible in an extremely broader speed range from 11.6 m/s to 27.9 m/s to support 8× recording.
Meanwhile, for the increased maximum recording speed, a recording layer material needs to be changed to a material that is more suitable for high-speed recording. Phase-change materials are generally used as the recording layer material of optical discs typified by DVD-RWs and CD-RWs. For such phase-change materials, alloys that can switch between an amorphous state and a crystalline state in a reversible manner are generally used. To achieve speed up, phase-change materials that rapidly switch from an amorphous state to a crystalline state, i.e., those with high crystallization rates need to be used. Increasing the crystallization rate, however, makes the control of the crystalline state at low-speed recording very difficult. For this reason, a major recording method (or write strategy) change needs to be made between the speed range close to the maximum and the speed range close to the minimum. Thus, using recording layer materials that support high-speed recording makes it very difficult to achieve recording at any recording speed below the maximum speed.
Examples of related art which may be associated with the present invention are as follows: for example, Japanese Patent Application Laid-Open (JP-A) No. 2005-78662 discloses an optical information recording method and an apparatus, where the delay amount of the first pulse is changed in the CAV recording by using a 2T strategy, and also discloses the fact that parameters are set for recording speed using linear functions; JP-A No. 2000-322740 discloses a method of recording to an optical recording medium, where parameters are set for recording speed using linear functions; and JP-A No. 2001-118245, JP-A No. 2001-243626, “DVD+ReWritable 4.7 Gbytes Basic Format Specifications System Description version 1.2” and “Recordable Compact Disc Systems Part III, volume 2, version 1.1” disclose an information recording method for setting parameters for recording speed using linear functions, an apparatus, and a technology for changing the parameters stepwise.
The related arts described above all fail to describe discontinuous pulse change, which is the feature of the present invention.
In addition, although JP-A No. 2003-281722 discloses a technology for changing the pulse number depending on the speed range for recording, its setting is totally opposite of the setting disclosed in the present invention; therefore it never reveals the present invention.